In modern data processing environments, a client's data is often distributed among a plurality of heterogeneous database systems. "Heterogeneous database systems" are database systems that have different data definition and manipulation procedures, security procedures, system management approaches, capabilities, etc. Examples of "heterogeneous database systems" include DB2 produced by International Business Machines (IBM) Corporation, Oracle produced by Oracle Corporation, Sybase produced by Sybase, Inc. etc. Such heterogeneous database systems, when used together, collectively represent a heterogeneous, distributed database environment (or system). Heterogeneous, distributed database systems are also sometimes called federated database systems and/or multi-database systems.
In order to enhance user-friendliness, it is preferred that clients be provided with a common interface to all of the heterogeneous database systems (also called back-end servers, back-end database systems, or simply back-ends). In other words, it is preferred that clients be under the illusion that they are interacting with a single back-end database system.
One conventional approach for achieving this goal is to introduce an interface module between the clients and the back-end database systems. This interface module, also called database middleware attempts to provide to clients transparent access to the back-end database systems. One example of the interface module is IBM DataJoiner. Generally speaking, the interface module receives data definition and manipulation instructions from clients. The interface module translates these instructions such that they are understandable to the appropriate back-end database systems, and then transfers the translated instructions to the appropriate back-end database systems. Similarly, the interface module translates information and messages received from the back-end database systems such that they are understandable to the appropriate clients, and then transfers the translated information and messages to the appropriate clients.